One of the menu options under the Contact Overview menu that is accessible when within a contact record is the Know Your Client section of the contact record:
After clicking Know Your Client, you'll then see the Know Your Client area for the contact and can begin filling in your applicable information for them.
Here, let's look at the Estimated Tax Information section of this page:
If no data has been entered here, it will be blank as above. To add data, just click the Edit button in the top right corner of this section. You'll then see the below:
Enter the client's AGI, Estimated Taxes, whether or not the data is confirmed by a Tax Return, the Tax Year and the Estimated Tax Bracket here and this section will look similar to the below, based upon your numbers:
Note: Adjusted Gross Income and Estimated Taxes are fields that you can include in any Custom Exports you build.